Products featuring organic and polymeric light-emitting devices (OLEDs and PLEDs) were first introduced into the market in 1999 and in 2002. Attracted by many advantages over LCD technology such as simple structure, thin-layer thickness, light-weight, wide viewing angle, low operating voltage, and possibility of producing large area display, over 100 manufacturers are engaged in the OLED and PLED development.
Organic materials including both small molecules and polymers have been employed to fabricate the devices. Developers of small molecules include Eastman Kodak Co., Idemitsu Kosan Co. Ltd., Sony Chemicals Corp., and Universal Display Corporation (UDC). Developers of polymers include Cambridge Display Technology (CDT), Dow Chemical Co., and Covion Organic Semiconductors GmbH.
Organic polymers provide considerable processing advantages over small molecules especially for the large area display. By using spin-coating or ink-jet printing method, the devices can be easily fabricated. However, blue-light PLEDs show some technical problems. These include design shortcoming, difficulties in purifying polymers, color purity problems, low efficiencies (maximum efficiency ˜2.5 cd/A) and short lifetime of devices (˜200 hrs at 20 mA/cm2 (lifetime to half brightness)).
Among the promising materials for use as emitting layers in PLEDs, poly(phenylene vinylene) (PPV) (U.S. Pat. No. 5,747,182) and PPV derivatives such as poly(2-methoxy-5-(2′-ethylhexyloxy-1,4-phenylenevinylene) (MEH-PPV) (U.S. Pat. No. 5,401,827; U.S. Pat. No. 6,284,435) have been disclosed. Other suitable materials include poly(p-phenylene) (PPP) and related derivatives (Angew. Chem., Int. Ed., 37, 402, (1998); Adv. Mater., 11, 895, (1999)), polythiophene and related derivatives (Macromolecules, 28, 7525, (1995)), polyquinoline and related derivatives (Macromolecules, 35, 382, (2002); Macromolecules, 34, 7315, (2001)), and polyfluorene (PFO) and related derivatives (WO 01/62822 A1; U.S. Pat. No. 6,169,163; Macromolecules, 35, 6094, (2002)). Generally, PPV-based materials demonstrate high PL and EL efficiencies, and color turning properties. However, long-term stabilities of their EL devices are obstructed due to the photooxidative degradation. Poly(p-phenylene)s are relatively insoluble and infusible. Polythiophene and related derivates have been shown to turn the electroluminescence from blue to near-infrared but generally have low quantum efficiencies. Polyfluorenes have liquid crystalline properties that lead to rapid degradation of device performance.
It is therefore desirable to develop a robust polymeric system which can provides new sights into the design of effective light-emitting polymers, and which can be use as a high performance emissive or host materials in electroluminescence devices.
2,2′:6′,2″-terpyridine (terpy) has received considerable attention as strong chelating agent to metal ions in recent years. In particular with transition metals, these metal-terpy polymers have been of great interest regarding their redox behaviors and photophysical properties.
Rehahn et al. reported rod-like ruthenium (II) coordination polymer via the reaction between ruthenium (III) trichloride and terpyridine-based monomer. The intrinsic viscosity of the high-molecular-weight polymer is of order of 300 mLg−1. Poly(p-phenylenevinylene) and polyimides which contain bis(2,2:6′,2″-terpyridine) ruthenium (II) complexes in their main chains and poly(phenylenevinylene) incorporated with pendent ruthenium terpyridine complexes have been synthesized and characterized by Chan and co-workers (Appl. Phys. Lett., 71, 2919, (1997); Chem. Mater., 11, 1165, (1999); Adv. Mater., 11, 455, (1999)). Vinyl substituted 2,2′:6′,2″-terpyridine and bifunctional ruthenium (II)-terpyridine complex polymers were prepared (Macromol. Rapid Commun., 23, 411, (2002)).
The design and synthesis of terpyridine-based dendrimers has been another attractive field. Poly(amido amine) dendrimer with external terpyridine units and its iron (II) complexes have been reported (Macromol. Rapid Commun., 20, 98, (1999)). Terpyridy-pendent poly(amido amine) and bis(terpyridine) containing ligands with Fe2+ or Co2+ ions were prepared by Abruña et al. (J. Phys. Chem. B, 105, 8746, (2001)). Some metallocentric dendrimers and metallodendrimers have been disclosed by Constable et ail (Chem. Commun., 1073, (1997)).
Besides, Khan et al. reported platinum (II) poly-yne which contain terpyridyl linker groups in their main chains (J. Chem. Soc., Dalton Trans., 1358, (2002)). These polymeric materials exhibit decreasing stabilities with increasing number of pyridine units in their backbones. Optically active poly(L-lactide)s, end-capped with terpyridyl group, have been prepared by Schubert et al. (Macromol. Rapid Commun., 22, 1358, (2001)). Under phase-transfer conditions, iron (II)-centered poly(L-lactide)s have been synthesized. Also, Schubert and co-workers have prepared zinc and cobalt metal containing copolymers with terpyridine segments of poly(ethylene oxide) and poly(oxytetramethylene). However, only UV-vis, GPC and NMR studies were reported. Perylene bisimide-based polymer bearing bis(terpyridine) groups were performed by Würthner et al. (Chem. Commun., 1878, (2002)).
In this invention, polymers based on the metal-induced and self-assembling system were prepared by simple reactions between zinc ions and terpyridine-based monomers. The octahedral coordinating geometry of the metal complex leads to the formation of stable linkages along the polymer chains. These metallo-supramolecules with well-defined architectures provide strong emissions from violet to blue, green, or yellow color with high quantum efficiencies.